1. Field of the Invention
The present invention relates to a display panel comprising a band of posters which has its two ends wound on a pair of spools, respectively, one being the feed spool when the other is the take-up spool, and vice-versa.
A known problem in the art is to find some means for compensating or correcting the poster band "drift" due to the local and irregular elongation or shrinking of the poster as a consequence of particular temperature, humidity or other conditions, including the prolonged exposure to sun rays, this elongation or shrinking being more marked in the case of a poster having one half exposed to sunlight and the other half kept in the shadow. Moreover, the spools are not always strictly parallel and the paper is not always exactly perpendicular to the spool axis, these factors further assisting in increasing the drift. Consequently, the poster band tends to slide on one or the other side during the winding thereof; if the band tends to become elongated on one side, a marked buckling of this side will be observed on the take-up spool, due to the decrease in the paper tension. Under these conditions, the paper will tend to coil up with a certain taper, since the band of posters is drifted transversely from the base of the cone, where the buckling takes place, to the top of the cone.
2. Description of the Prior Art
In the U.S. Pat. No. 3,726,031 delivered to Singer a typical solution of this problem is proposed. This patent discloses a poster or display panel comprising a supporting panel and a band of posters wound at either end on a pair of driven spools, respectively, said driven spools being positioned behind the panel and said band of posters passing over a pair of intermediate rollers mounted for loose rotation and located at the top and bottom of the panel. The drift is corrected by inclining the two driven spools which remain constantly parallel to each other, by means of a relatively complicated mechanism; thus, the poster driven laterally on the intermediate rollers is properly re-centered.
To avoid the inconvenience of this lateral shift, the present invention provides means for reducing the tension exerted on the paper on the side opposite the buckling side, or, in other words, for creating on the side opposite said observed buckling another compensating effect buckling so as to change the orientation of said shift, which in any case is detected by means known per se.